Organic materials include a wide variety of carbon skeleton-based compounds. Among them, electrically conductive organic molecules particularly have been confirmed to exhibit versatile electrical properties that originate from their molecular structures. Various proposals have been made to use them for a variety of organic electronic device applications, such as thin film transistors, sensors, organic LEDs, capacitors, batteries, biofunctional devices, and lasers.
Thin film transistors (hereinafter also referred to as “TFTs”) are currently expected to be useful drive elements for such devices as active matrix liquid crystal displays. TFTs normally are formed of inorganic semiconductor materials, such as amorphous silicon and low-temperature polysilicon. Cost reductions and larger panel areas are possible by using organic molecules to form the semiconductor layer of a TFT.
Nevertheless, organic semiconductors that have been reported to date show lower carrier mobilities than those of inorganic semiconductors, and the device elements that use the organic semiconductors have problems such as high driving voltage. For this reason, much research effort has been directed to improvements in the carrier mobility of organic semiconductors and to reductions in driving voltage of device elements that use organic semiconductors.
Most field-effect transistors (hereinafter also referred to as the “FET”) that use organic semiconductor molecules fail to achieve desired device characteristics that are expected from inherent properties of the organic semiconductor molecules. One of the causes is as follows. Although the charge transfer within an organic semiconductor molecule is very fast, the charge transfer from one organic semiconductor molecule to another is slower than that. Consequently, the latter charge transfer speed restricts the overall performance of the semiconductor layer. As one of the means to improve this drawback, a semiconductor layer in which a conduction path is formed by fine particles made of a conductor or a semiconductor and organic semiconductor molecules bonded thereto has been disclosed (JP 2004-88090A).
On the other hand, an electronic device that uses a n-conjugated polymer as the electrically conductive organic molecules tends to be adversely affected by oxygen and water easily, and this requires an additional complication in that a sealing structure or the like needs to be provided in order to maintain the device characteristics. As one method for improving this drawback, a method for improving device reliability by enclosing a conductive polymer with an insulative cyclic molecule such as cyclodextrin has been disclosed (JP 2003-298067A).
According to the means described in JP 2004-88090A, either a conductor or a semiconductor may be selected as the microparticles. In terms of device design, it is preferable to use microparticles made of a conductor because simple device characteristics are obtained more easily when the semiconductor properties are exhibited using only an organic material. However, if the chain length of the organic semiconductor molecule is short relative to the particle size of the microparticles, the use of a conductor for the microparticles can result in the conductive microparticles contacting each other or hopping of charge carriers between the microparticles. As a consequence, the problems of short circuits and leakage current increases may arise. If the chain length of the organic semiconductor molecule is made longer in order to resolve the foregoing problems, another problem arises in that the linearity of the molecule becomes poor, which leads to entanglement of the organic semiconductor molecules with one another and bonding of opposing ends of the molecule to the same microparticle, and desired characteristics cannot be obtained.